TITLE: GCN CIRCULAR NUMBER: 18149 SUBJECT: GRB 150817A: Fermi GBM observation DATE: 15/08/17 15:37:57 GMT FROM: Hoi-Fung Yu at MPE H.-F. Yu (MPE) and P. Jenke (UAH) report on behalf of the Fermi GBM Team: "At 02:05:08.40 UT on 17 August 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150817A (trigger 461469912 / 150817087), which was also detected by the Swift/BAT (D'Elia et al. 2015, GCN 18143). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 102 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of multiple peaks with a duration (T90) of about 36 s (50-300 keV). The time-averaged spectrum from T0-10.240 s to T0+45.057 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.34 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 109.0 +/- 8.8 keV. The event fluence (10-1000 keV) in this time interval is (1.15 +/- 0.05)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+16.256 s in the 10-1000 keV band is 15.7 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."